U.S. patent number 10,191,204 [Application Number 15/540,575] was granted by the patent office on 2019-01-29 for materials and lightguides for color filtering in lighting units.
This patent grant is currently assigned to GE Lighting Solutions, LLC. The grantee listed for this patent is GE Lighting Solutions, LLC. Invention is credited to Matthew A. Bugenske, Dengke Cai, Yingchun Fu, Jianmin He, Xiaojun Ren, Chenjie Xu.
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United States Patent |
10,191,204 |
Fu , et al. |
January 29, 2019 |
Materials and lightguides for color filtering in lighting units
Abstract
Materials and lightguides formed thereof that are suitable for
use in lighting units to impart a color filtering effect to visible
light. At least a portion of such a lightguide (16) is formed of a
composite material comprising a polymeric matrix material and an
inorganic particulate material that contributes a color filtering
effect to visible light passing through the composite material, and
the particulate material comprises a neodymium compound containing
Nd.sup.3+ ions.
Inventors: |
Fu; Yingchun (Shanghai,
CN), Xu; Chenjie (Shanghai, CN), Ren;
Xiaojun (Shanghai, CN), Cai; Dengke (East
Cleveland, OH), He; Jianmin (East Cleveland, OH),
Bugenske; Matthew A. (East Cleveland, OH) |
Applicant: |
Name |
City |
State |
Country |
Type |
GE Lighting Solutions, LLC |
East Cleveland |
OH |
US |
|
|
Assignee: |
GE Lighting Solutions, LLC
(East Cleveland, OH)
|
Family
ID: |
56355403 |
Appl.
No.: |
15/540,575 |
Filed: |
January 6, 2015 |
PCT
Filed: |
January 06, 2015 |
PCT No.: |
PCT/CN2015/070191 |
371(c)(1),(2),(4) Date: |
June 29, 2017 |
PCT
Pub. No.: |
WO2016/109940 |
PCT
Pub. Date: |
July 14, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170336557 A1 |
Nov 23, 2017 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
6/0073 (20130101); G02B 5/206 (20130101); G02B
6/0015 (20130101); F21V 9/20 (20180201); G02B
6/0091 (20130101); G02B 6/0065 (20130101); G02B
1/04 (20130101); G02B 6/0041 (20130101); F21Y
2115/10 (20160801); G02B 6/006 (20130101); G02B
6/0095 (20130101); F21Y 2103/10 (20160801) |
Current International
Class: |
F21V
8/00 (20060101); G02B 5/20 (20060101); G02B
1/04 (20060101); F21V 9/00 (20180101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102201549 |
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Sep 2011 |
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CN |
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699 17 065 |
|
Apr 2005 |
|
DE |
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2 135 916 |
|
Dec 2009 |
|
EP |
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2 681 522 |
|
Jan 2014 |
|
EP |
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2 978 448 |
|
Feb 2013 |
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FR |
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2008/111878 |
|
Sep 2008 |
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WO |
|
Other References
Reben, Manuela, et al. "Nd3+-doped oxyfluoride glass ceramics
optical fibre with SrF." Optica Applicata 42.2 (2012). cited by
examiner .
Li, M., et al., "Controllable energy transfer in fluorescence
upconversion of NdF3 and NaNdF4 nanocrystals," Optic Express, vol.
18, No. 4, pp. 3364-3369 (Feb. 15, 2010). cited by applicant .
International Search Report and Written Opinion issued in
connection with corresponding PCT Application No. PCT/CN2015/070191
dated Sep. 25, 2015. cited by applicant .
European Search Report and Opinion issued in connection with
corresponding EP Application No. 15876450.6 dated Jul. 27, 2018.
cited by applicant.
|
Primary Examiner: Green; Tracie Y
Attorney, Agent or Firm: DiMauro; Peter T. GPO Global Patent
Operation
Claims
What is claimed is:
1. A lightguide of a lighting unit, at least a portion of the
lightguide being formed of a composite material comprising a
polymeric matrix material and an inorganic particulate material
that contributes a color filtering effect to visible light passing
through the composite material, the inorganic particulate material
comprising a neodymium compound containing Nd.sup.3+ ions, wherein
the neodymium compound is an Nd--F compound or an Nd--X--F compound
where X is at least one element chosen from the group consisting of
elements that form compounds with neodymium and elements other than
neodymium that form compounds with fluorine; wherein the lightguide
is configured to trap light received at an edge of the lightguide
through total internal reflection, and redirect trapped light to be
extracted from the lightguide at a surface thereof.
2. The lightguide according to claim 1, wherein the inorganic
particulate material contributes the color filtering effect to
visible light generated by an LED device.
3. The lightguide according to claim 1, wherein the inorganic
particulate material predominantly filters wavelengths in the
yellow light wavelength range.
4. The lightguide according to claim 1, wherein the neodymium
compound is present as discrete particles of the inorganic
particulate material.
5. The lightguide according to claim 1, wherein the neodymium
compound is present as a dopant in discrete particles of the
inorganic particulate material.
6. The optical component according to claim 1, wherein the
neodymium compound is an Nd--X--F compound, and X is at least one
element chosen from the group consisting of elements that form
compounds with neodymium and elements other than neodymium that
form compounds with fluorine.
7. The lightguide according to claim 1, wherein the polymeric
matrix material is chosen from the group consisting of
polycarbonate, polystyrene, polymethyl methacrylate, polyvinylidene
fluoride, and silicone.
8. The lightguide according to claim 1, wherein the neodymium
compound and the polymeric matrix material have refractive indices
within 0.1 of each other in the visible light region.
9. The lightguide according to claim 1, wherein the inorganic
particulate material and the polymeric matrix material have
refractive indices within 0.1 of each other in the visible light
region.
10. The lightguide according to claim 9, wherein the neodymium
compound is present as discrete particles of the inorganic
particulate material.
11. The lightguide according to claim 9, wherein the neodymium
compound is present as a dopant in discrete particles of the
inorganic particulate material, and the discrete particles are
formed of a second material other than the neodymium compound.
12. The lightguide according to claim 11, wherein the discrete
particles are formed of at least one material chosen from the group
consisting of metal fluorides and metal oxides having refractive
indices less than the polymeric matrix material.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to lighting systems and
related technologies. More particularly, this invention relates to
materials and methods suitable for imparting color filtering
effects to light sources, nonlimiting examples of which include
edge-lit lighting units comprising a lightguide coupled with a
light source (for example, one or more light-emitting diodes
(LEDs)) at an edge of the lightguide.
LED lamps (bulbs) are capable of providing a variety of advantages
over more traditional incandescent and fluorescent lamps, including
but not limited to a longer life expectancy, high energy
efficiency, and full brightness without requiring time to warm up.
As known in the art, LEDs (which as used herein also encompasses
organic LEDs, or OLEDs) are solid-state semiconductor devices that
convert electrical energy into electromagnetic radiation that
includes visible light. An LED typically comprises a chip (die) of
a semiconducting material doped with impurities to create a p-n
junction. The LED chip is electrically connected to an anode and
cathode, all of which are often mounted within a package. LEDs emit
visible light that is more directional in a narrower beam as
compared to other light sources such as incandescent and
fluorescent lamps. As such, LEDs have traditionally been utilized
in applications such as automotive, display, safety/emergency, and
directed area lighting. However, advances in LED technology have
enabled high-efficiency LED-based lighting systems to find wider
use in lighting applications that have traditionally employed other
types of lighting sources, including omnidirectional lighting
applications previously served by incandescent and fluorescent
lamps. As a result, LEDs are increasingly being used for area
lighting applications in residential, commercial and municipal
settings.
FIGS. 1 and 2 schematically represent a portion of an edge-lit
light fixture or luminaire 10 that includes a light source 12 (FIG.
2) disposed in a fixture housing 14. The light source 12 is
represented in FIG. 2 as comprising an LED device, which can be one
of any number of LEDs in an array within the fixture housing 14,
with the LEDs typically facing in the same direction and each LED
effectively being a discreet point light source. As such, the
fixture housing 14 is configured to point the LED devices 12 in a
direction to direct the light emanating from the luminaire 10. As a
nonlimiting example, the luminaire 10 can be configured to
illuminate the shelving and contents of a commercial refrigerated
display case. Another type of edge-lit luminaire is referred to as
a recessed troffer, which is commonly used for drop ceilings in
commercial and retail space. Still other applications for edge-lit
luminaires include signage, an example of which is "exit" signs
commonly used in commercial and retail space.
For illumination applications of the types noted above, the
luminaire 10 is shown as further comprising a lightguide 16 having
an edge 18 (FIG. 2) disposed in proximity to the array of LED
devices 12. As known in the art, the lightguide 16 is an optic
component commonly employed in edge-lit technologies. Lightguides
are formed to have a surface microstructure adapted to achieve
total internal reflection (TIR) to direct light from a light source
to a desired application space. The lightguide 16 may be visible
from multiple directions, and is typically desired to have a
uniform luminance while illuminating a specified area with a
desired light level. Depending on the particular application,
materials commonly employed to produce lightguides include optical
grade transparent materials such as acrylics, though various other
materials may be used, for example, polyamides (nylon),
polycarbonate (PC), polystyrene (PS), and polypropylene (PP).
Because LED devices emit visible light in narrow bands of
wavelengths, for example, green, blue, red, etc., combinations of
different LED devices are often combined in LED-based lamps to
produce various light colors, including white light. The LED
devices are often mounted on a carrier, and may be encapsulated on
the carrier, for example, with a protective cover, often formed of
an index-matching material to enhance the efficiency of visible
light extraction from the LED devices. As a nonlimiting example,
FIG. 2 represents the LED device 12 mounted on a carrier 20 and
enclosed by a dome 22 that serves as an optically transparent or
translucent envelope enclosing an LED chip (not shown) on the
carrier 20. A phosphor may also be used to emit light of color
other than what is generated by an LED. For this purpose, the inner
surface of the dome 22 may be provided with a coating that contains
a phosphor composition, in which case electromagnetic radiation
(for example, blue visible light, ultraviolet (UV) radiation, or
near-visible ultraviolet (NUV) radiation) emitted by the LED chip
can be absorbed by the phosphor composition, resulting in
excitation of the phosphor composition to produce visible light
that is emitted through the dome 22. As an alternative, the LED
chip may be encapsulated on the carrier 20 with a coating, and such
a coating may optionally contain a phosphor composition for
embodiments in which LED-phosphor integration with LED epitaxial
(epi) wafer or die fabrication is desired.
Though the use of combinations of different LED devices and/or
phosphors can be utilized to promote the ability of luminaires
equipped with lightguides to produce desired lighting effects,
certain desirable lighting effects can be somewhat challenging to
achieve with such approaches. A notable example is the lighting
effect achieved with the REVEAL line of incandescent bulbs
commercially available from GE Lighting, which are produced to have
an outer jacket formed of a glass doped with neodymium oxide
(neodymia, Nd.sub.2O.sub.3) to filter certain wavelengths of light.
Lighting effects similar to that achieved with the REVEAL line of
incandescent bulbs would also be desirable for luminaires equipped
with lightguides.
BRIEF DESCRIPTION OF THE INVENTION
The present invention provides materials and lightguides formed
thereof that are suitable for use in lighting units to impart color
filtering effects to light sources, and particularly edge-lit
lighting units comprising lightguides coupled with LED-based light
sources.
According to one aspect of the invention, at least a portion of a
lightguide is formed of a composite material comprising a polymeric
matrix material and an inorganic particulate material that
contributes a color filtering effect to visible light passing
through the composite material, and the particulate material
comprises a neodymium compound containing Nd.sup.3+ ions.
According to another aspect of the invention, a lighting unit
includes a light source that emits visible light and a lightguide
configured and arranged so that at least a portion of the visible
light of the light source passes therethrough. The portion of the
lightguide is formed of a composite material comprising a polymeric
matrix material and an inorganic particulate material that
contributes a color filtering effect to the visible light passing
through the portion, and the particulate material comprises a
neodymium compound containing Nd.sup.3+ ions.
Additional aspects of the invention include utilization of a
composite material of a type described above, wherein the neodymium
compound can be present as discrete particles or as a dopant in the
particulate material to promote refractive index matching of the
particulate material and the polymeric matrix material sufficient
to impart a low-haze optical effect to visible light emitted by the
lighting unit, believed to be due at least in part to minimizing
Mie scattering.
Technical effects of the composite materials, lightguides, and
lighting units described above preferably include the capability of
providing a desirable color filtering effect, and preferably with
the capability of matching the refractive index of the matrix
material to minimize optical scattering of light passing through
the composite materials and lightguides.
Other aspects and advantages of this invention will be better
appreciated from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically represents a perspective view of an edge-lit
luminaire of a type capable of benefitting from the inclusion of a
lightguide containing a neodymium-fluoride composition in
accordance with a nonlimiting embodiment of this invention.
FIG. 2 schematically represents a partial cross-sectional view of
the edge-lit luminaire of FIG. 1.
FIG. 3 is a graph representing the absorption spectra observed for
NdF.sub.3 and NaNdF.sub.4 nanocrystals, and
FIG. 4 is a graph representing the upconversion fluorescence
spectra for NdF.sub.3 and NaNdF.sub.4 nanocrystals when subjected
to an excitation frequency (.lamda..sub.exc) of 800 nm and an
excitation power of 240 mW.
FIG. 5 is a graph representing optical transmission characteristics
of NdF.sub.3 dispersed in a silicone matrix, in comparison to that
of an Nd.sub.2O.sub.3-doped glass.
DETAILED DESCRIPTION OF THE INVENTION
The following discussion will make reference to the LED-based
luminaire 10 represented in FIGS. 1 and 2. However, it should be
appreciated that lighting units and LED devices of various other
configurations are also within the scope of the invention.
As previously discussed, the luminaire 10 represented in FIGS. 1
and 2 includes an array of LED devices 12, one of which is
schematically depicted in FIG. 2. The LED devices 12 serve as the
light source or light engine of the edge-lit luminaire 10. Any
number of LED devices 12 can be utilized with the luminaire 10,
with the number and spacing therebetween depending on the desired
amount of light output and the distribution of light desired. The
luminaire 10 may be one of a plurality of luminaires arranged and
potentially assembled together to provide a fixture with a desired
light output level.
As previously discussed in reference to FIG. 2, each LED device 12
can be enclosed by a dome 22 and mounted on a carrier 20 located in
a cavity 24 within the fixture housing 14. An edge portion of the
lightguide 16 is received through an opening 30 in the housing 14
and secured within the opening 30 so that the lightguide edge 18 is
located in proximity to, though typically spaced apart from, the
LED devices 12. The housing 14 is represented as containing optics
26, for example, reflectors and/or lenses, for directing light from
the LED devices 12 toward the edge 18 of the lightguide 16. Various
constraints known in the art exist for the type, size, shape, and
placement of the optics 26 relative to the LED devices 12 and the
lightguide edge 18, for example, to promote optical efficiency by
maximizing coupling of the lightguide 16 with light emitted from
the LED devices 12, and such constraints will not be discussed in
any detail here.
The housing 14 can have any suitable shape, and is therefore not
limited to the cross-sectional shape represented in FIGS. 1 and 2.
The housing 14 will typically be equipped with various other
features and hardware necessary for its intended use. For example,
the housing 14 may include a heat sink (not shown) for conducting
heat away from the LED devices 12, various features and hardware
for mounting the luminaire 10 to a support surface, electrical
wiring for connecting the LED devices 12 to a power source,
etc.
As known in the art, the lightguide 16 preferably serves to trap
light received at its edge 18 through total internal reflection
(TIR), and redirect the trapped light out of the lightguide 16 as a
result of the presence of defects or other light-extracting
features located at surfaces 28 of the lightguide 16, preferably
limited to surface regions outside the housing 14 to inhibit losses
from the edge portion of the lightguide 16 within the housing 14.
As known in the art, the light-extracting features extract light
from the lightguide 16 that would otherwise be trapped within the
lightguide 16 due to total internal reflection. Various approaches
and aspects are known in the art as to the creation and
configuration of light-extracting features for use in lightguides,
and will not be discussed in any detail here.
The lightguide 16 is represented in FIGS. 1 and 2 as having a blade
configuration characterized a rectangular cuboid or parallelepiped
shape, though other three-dimensional shapes are also within the
scope of the invention. The width of the edge 18 exposed to the
light within the housing 14 can also vary, with widths of about
four millimeters being a known example. Though the surfaces 28 of
the lightguide 16 are represented as being planar and entirely free
of any features (other than light-extracting features), the
surfaces 28 may be modified to achieve certain illumination effects
desired of the luminaire 10, for example, features that enable the
luminaire 10 to function as signage, such as modifying certain
light-extracting features or applying a film to the surfaces 28 to
define, for example, letters, symbols, or graphics.
The present invention provides composite materials suitable for use
as lightguides (including the lightguide 16 of FIGS. 1 and 2) and
capable of imparting a color filtering effect to visible light
emitted by a lightguide, particularly visible light generated by
one or more LED devices. The composite materials contain a source
of Nd.sup.3+ ions, which through investigations leading to the
present invention has been determined to be effective for providing
a color filtering effect, in particular to filter visible light in
the yellow light wavelength range, for example, wavelengths of
about 0.56 to about 0.60 micrometers.
According to certain aspects of the invention, such composite
materials and lightguides produced therefrom may have little if any
optical scattering (diffusion) effect, depending on the composition
of the composite material. As examples, preferred composite
materials comprise an optical grade transparent material as a
polymeric matrix material, in which is dispersed an inorganic
particulate material containing the source of Nd.sup.3+ ions. The
Nd.sup.3+ ion source may be a neodymium compound present as a
dopant in the particulate material, or as discrete particles that
may be optionally combined with discrete particles of other
materials to make up the particulate material. A particulate
material containing discrete particles of the neodymium compound
(e.g., formed partially or entirely of the neodymium compound)
and/or discrete particles doped with the neodymium compound can be
combined with a polymeric matrix material for the purpose of
promoting refractive index matching of the particulate and
polymeric matrix materials (i.e., minimize the difference in their
refractive indices) sufficient to impart a low-haze
(low-diffusivity) optical effect to visible light passing through
the composite material.
A preferred source for the Nd.sup.3+ ions is believed to be Nd--F
containing materials having a relatively low refractive index. A
particularly preferred Nd.sup.3+ ion source is believed to be
neodymium fluoride, NdF.sub.3, which has a refractive index of
around 1.6, providing a suitably low refractive index for index
matching with certain polymeric matrix materials to minimize
scattering losses. Other Nd.sup.3+ ion sources are possible, for
example, other compounds containing Nd--F, nonlimiting examples of
which include Nd--X--F compounds where X is at least one element
that forms a compound with neodymium, as examples, oxygen,
nitrogen, sulfur, chlorine, etc., or at least one element (other
than Nd) that forms a compound with fluorine, as examples, metals
such as Na, K, Al, Mg, Li, Ca, Sr, Ba, and Y, or combinations of
such elements. Particular examples of Nd--X--F compounds include
neodymium oxyfluoride (Nd--O--F) compounds formed of Nd--F
(including NdF.sub.3) and Nd--O compounds (including
Nd.sub.2O.sub.3), Nd--X--F compounds in which X may be Mg and Ca or
may be Mg, Ca and O, as well as other compounds containing Nd--F,
including perovskite structures doped with neodymium. Certain
Nd--X--F compounds may advantageously enable broader absorption at
wavelengths of about 580 nm. For example, depending on the relative
amounts of Nd--O and Nd--F compounds, an oxyfluoride compound may
have a refractive index that is between that of the Nd--O compound
(for example, 1.8 for neodymia) and Nd--F compound (for example,
1.60 for NdF.sub.3). Nonlimiting examples of perovskite structure
materials doped with neodymium include those containing at least
one constituent having a lower refractive index than the neodymium
compound (e.g., NdF.sub.3), for example, metal fluorides of Na, K,
Al, Mg, Li, Ca, Sr, Ba, and Y. Such host compounds have lower
refractive indices than NdF.sub.3 in the visible light region,
nonlimiting examples of which include NaF (n=1.32), KF (n=1.36),
AlF.sub.3 (n=1.36), MgF.sub.2 (n=1.38), LiF (n=1.39), CaF.sub.2
(n=1.44), SrF.sub.2 (n=1.44), BaF.sub.2 (n=1.48), and YF.sub.3
(n=1.50) at a wavelength of 589 nm. As a result of doping with a
high refractive index Nd--F compound, for example, NdF.sub.3, the
resulting doped perovskite structure compound has a refractive
index that is between that of the host (for example, 1.38 for
MgF.sub.2) and NdF.sub.3 (1.60). The refractive index of the
NdF.sub.3-doped metal fluoride compound will depend on the ratio of
Nd ions and metal ions.
Generally, a low-haze (low-diffusivity) optical effect due to a
minimal level of optical scattering is said to be achieved herein
if the refractive indices of the matrix and particulate materials
are within 0.1 of each other in the visible light region. If
NdF.sub.3 is used as the sole inorganic particulate material in a
lightguide whose polymeric matrix material is a polycarbonate (PC)
or polystyrene (PS), the refractive indices of NdF.sub.3 (about
1.60) and PC and PS (about 1.586) are such that a minimal level of
optical scattering occurs when light passes through the component.
Another example of a polymer having a refractive index within 0.1
of NdF.sub.3 is a fluorine-doped polyester (refractive index of
about 1.607). In this regard, the polymeric matrix material is
chosen on the basis of having a refractive index that is similar to
the neodymium compound so as to achieve a low-haze
(low-diffusivity) optical effect.
Refractive index matching with other polymers having refractive
indices that differ from the neodymium compound in the visible
light region by more than 0.1 can be achieved with modifications to
the particulate material. For example, the source of Nd.sup.3+ ions
(e.g., NdF.sub.3) can be used in combination with one or more other
materials to yield an effective refractive index that achieves a
minimal level of optical scattering in a lightguide whose polymeric
matrix material has a refractive index that differs from the
Nd.sup.3+ ion source by more than 0.1 in the visible light region,
for example, acrylics (for example, polymethyl methacrylate; PMMA),
polyvinylidene fluoride (PVDF), and silicones. As a nonlimiting
example, particles formed of a metal fluoride and/or a metal oxide
can be doped with the neodymium compound to have a refractive index
between that of the neodymium compound and the metal fluoride
and/or metal oxide. Nonlimiting examples of suitable metal
fluorides and metal oxides include NaF (refractive index of about
1.32) and MgF.sub.2 (refractive index of about 1.38). By selecting
an appropriate co-solidation ratio of the neodymium compound and
the metal fluoride and/or metal oxide, the refractive index of the
particulate material can be tailored to allow for matching or near
matching with the refractive index of PMMA (about 1.49),
polyvinylidene fluoride (about 1.42), or a methyl-type silicone
(about 1.41), which are often utilized in LED packages.
FIGS. 3 and 4 are graphs published in "Controllable Energy Transfer
in Fluorescence Upconversion of NdF.sub.3 and NaNdF.sub.4
Nanocrystals", Li et al., Optics Express, Vol. 18 Issue 4, pp.
3364-3369 (2010), and represent optical properties for NdF.sub.3
and NaNdF.sub.4 nanocrystals dispersed in water at the same molar
concentration. FIG. 3 represents the absorption spectra observed
for the NdF.sub.3 and NaNdF.sub.4 nanocrystals, and FIG. 4
represents the upconversion fluorescence spectra for the NdF.sub.3
and NaNdF.sub.4 nanocrystals when subjected to an excitation
frequency (.lamda..sub.exc) of 800 nm and an excitation power of
240 mW. As evident from FIG. 3, the absorption peaks of NdF.sub.3
and NaNdF.sub.4 were 578 and 583, respectively, and therefore well
within the yellow light wavelength range (about 560 to about 600
nm), and FIG. 4 evidences that the absorption peaks of NaNdF.sub.4
were slightly shifted relative to those of NdF.sub.3. FIGS. 3 and 4
indicate that co-solidation of NdF.sub.3 and NaF (to yield
NaNdF.sub.4) did not fundamentally change the absorption
characteristics of NdF.sub.3. As such, it is believed that a
desirable color filtering effect can be achieved with composite
materials containing particles containing a compound other than
Nd--F that has been doped with an Nd--F compound to yield an Nd-M-F
compound (where M is a metal other than neodymium).
The color filtering effect resulting from visible light absorption
provided by Nd.sup.3+ ions in the visible light spectrum is
believed to be superior to Nd--O compounds (such as
Nd.sub.2O.sub.3) with respect to yellow light wavelengths within
the range of 0.56 to about 0.60 micrometers. Nd--F and Nd--X--F
compounds have a further advantage over Nd--O compounds by having a
refractive index much closer to various standard optical grade
transparent plastics, for example, PC, PS, PMMA, PVDF, silicone,
and polyethylene terephthalate (PET), and can better balance
optical losses from scattering attributable to refractive index
mismatch and Nd ion absorption. By filtering yellow light
wavelengths, light emitted by an array of white LED devices can be
adjusted to achieve an enhanced color effect by separating green
and red light through filtering yellow light wavelengths, such as
by increasing LED white light CRI (color rendering index), CSI
(color saturation index) and enabling color points closer to the
white locus. A notable example of such a desirable lighting effect
is achieved with the REVEAL line of incandescent bulbs commercially
available from GE Lighting, which are produced to have an outer
jacket formed of a glass doped with neodymia (Nd.sub.2O.sub.3) to
filter certain wavelengths of light. FIG. 5 is a graph representing
the optical transmission of NdF.sub.3 dispersed in a silicone
matrix in comparison to that of an Nd.sub.2O.sub.3-doped glass, and
evidences the similarities in their optical transmissions,
particularly in terms of their abilities to filter yellow light
wavelengths.
The volumetric amount and particle size of the particulate source
of Nd.sup.3+ ions in a composite material is believed to have an
influence on the color filtering effect of the composite material.
In addition, the relative amounts and particle size of any second
material in the composite material have an influence on the color
filtering effect. Generally, it is believed that a composite
material formed of a standard optical grade transparent plastic
(for example, PC, PS, PMMA, PVDF, silicone, or PET) should contain
at least 0.1 volume percent and more preferably about 1 to about 20
volume percent of NdF.sub.3 or a comparable Nd.sup.3+ ion source
(as examples, Nd--F compounds and Nd--X--F compounds, including
MgF.sub.2 doped with Nd--F) to achieve a desired filtering effect.
It is further believed that a suitable particle size for the
particulate material is up to about 50 micrometers and preferably
about 0.5 to about 5 micrometers. At these loadings and particles
sizes, a composite material whose matrix material is one of the
aforementioned standard optical grade transparent plastics will
typically be readily moldable for a wide variety of shapes, with
potential difficulties being encountered with smaller particle
sizes and higher loadings.
While the invention has been described in terms of certain
embodiments, it is apparent that other forms could be adopted by
one skilled in the art. Therefore, the scope of the invention is to
be limited only by the following claims.
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